The invention relates to an observation instrument comprising a hollow body having a specific internal diameter, wherein an optoelectronic image recording system is arranged in an end region of the hollow body and has on the image entrance side an optical lens system having a cylindrical section and subsequently an image sensor, which converts the image coming from the optical lens system into electrical image signals, wherein the optical axis of the lens system extends in the direction of the longitudinal axis of the hollow body, wherein the external diameter of the cylindrical section of the lens system is less than the internal diameter of the hollow body, to be precise such that between an inner side of the hollow body and the outer side of the optical lens system a sufficient interspace remains, through which further components can be led in the hollow body, wherein with a viewing direction of greater than 0° to less than 90° from the optical axis of the image system a distal deflection prism is arranged on the image entrance side at the lens system.
Such observation instruments comprising a hollow body in the form of a shank are used in particular as endoscopes or as exoscopes. DE 10 2010 007 394 A1 discloses a medical observation instrument having an optoelectronic image recording system arranged in its shank in the distal end region.
In numerous observation instruments, the viewing direction runs straight ahead, that is to say that it runs in the longitudinal axis of the shank. In some fields of use, particularly in the medical field, however, it is desirable for such observation instruments to have a viewing direction which deviates from the rectilinear viewing direction, the so-called 0° viewing direction, wherein the viewing direction deviates from the rectilinear viewing direction by between 0° and up to 90°.
As a result, cavities, such as the interior of a bladder, for example, can be examined spaciously, particularly if the rectilinearly and longitudinally extending shank has to be introduced through a channel of long extent, for example a urethra, into said cavity to be observed.
The optical axis of the actual lens system that guides the entering image to the optical sensor extends in the direction of the longitudinal axis of the shank. As a result, it is possible to produce the lens systems by means of customary lenses having a circular cross section.
In order that the light or image arriving from the inclined viewing direction can then be fed to this lens system extending in the optical axis, a distal deflection prism is arranged on the image entrance side at the lens system. Said deflection prism has the task of feeding the light or image rays arriving at the respective viewing angle of between 0° and 90° to the optical lens system as far as possible in the direction of the optical axis.
In the case of these observation instruments, the image is projected by the optical lens system onto an image sensor that converts the optical image information into electrical image signals. Said electrical image signals are then fed via corresponding lines to an image conversion system or to a monitor.
The technology of image sensors has undergone considerable development in recent years, particularly as far as the resolution is concerned. In this regard, high-resolution image sensors having pixel sizes of less than 3 μm are already commercially available at the present time.
The hollow shanks of observation instruments have a diameter which is substantially determined by the size of the opening through which the shank of the observation instrument can be led.
Particularly in the medical field, said openings are predefined by specific organs, for example by the diameter of a urethra or the anatomy of the person in whom observation is to take place.
In this regard, by way of example, shanks that can be used for children have significantly smaller diameters than those for adults. In the ENT field and also in brain surgery, often only openings or channels having very small diameters are available for introducing such hollow shanks of observation instruments.
In numerous cases, the observation instrument is not just purely an observation instrument, rather medical interventions are intended also to be able to be performed by means of the shank. Therefore, the optoelectronic image recording system cannot occupy the entire inner lumen of the hollow body, but rather only parts thereof, such that alongside the optoelectronic image recording system a sufficiently large interspace also remains for leading through further components.
Since, by way of example, instruments are led through said interspace, which instruments carry away contaminated tissue from inside the body after the intervention through the shank, it is necessary to ensure that hermetic sealing between the optoelectronic image recording system and said interspace is effected, in order that no contaminations or contaminants can penetrate into this system. Furthermore, this system has to be hermetically separated from the interspace additionally because said interspace has to be rinsed, cleaned and disinfected after an intervention. The chemically aggressive media used in this case might damage the optoelectronic system.
Therefore, the so-called multi-tube technique is employed in this technology. That means that the optoelectronic image recording system is integrated into an inner shank, which is introduced into the actual hollow body, which is then designated as the outer shank. In this case, customary arrangements include those in which the inner shank is either arranged coaxially in the outer shank, such that a ring-shaped interspace remains around its outer side, through which interspace further components or instruments or else other shanks can then be led. Alternatively, the inner shank is arranged along a surface line on the inner side of the outer shank, such that a crescent-like interspace remains. Accordingly, the external diameter of the cylindrical section of the lens system usually corresponds to the internal diameter of an inner shank inserted into the actual hollow body.
In the observation systems having viewing directions that deviate from the rectilinear 0° viewing direction, the distal deflection prism is required. Since the latter is likewise arranged in the optoelectronic image recording system hermetically sealed from the interspace, its radial extent is likewise restricted to the diameter of the cylindrical section since it is accommodated in said inner shank or a corresponding sleeve surrounding said section of the optical system.
It has now been established that as a result of the further development of the high-resolution image sensors by means of such an optoelectronic image recording system, the image information conducted to the image sensor is less than the latter could actually handle. The high resolution is determined by the so-called numerical aperture, that is to say the angle formed by an image beam which impinges on a pixel point of the image sensor. The higher the numerical aperture, that is to say the greater said angle, the sharper and more highly resolved the pixel.
It has now been established in practical use that with the predefined dimensions, that is the diameter of the optical lens system, the amount of image information that can be conducted to a high-resolution image sensor is not as much as the latter can acquire.
One solution to the problem would be to increase the diameter of the optical lens system with the image recording area and resolution of an image sensor remaining the same. This is impractical, however, since otherwise the interspace between the optoelectronic image recording system and the inner side of the hollow body would become small, and so instruments could no longer be led through or not enough optical fibres for the illumination could be led to distal.
As already mentioned, the size or the diameter of the outer shank is determined by the opening into which such a shank of an observation instrument can be inserted. In the field of technical endoscopy, by way of example that would include existing holes, for example for examining the interior of a combustion chamber or the like, which cannot be enlarged for any reasons.
It is therefore an object of the present invention to remedy this and to improve an observation instrument of the type mentioned in the introduction having a viewing direction which deviates from the rectilinear viewing direction, to the effect that so much image information can be introduced that the capabilities even of high-resolution image sensors can be utilized, in particular image sensors having pixel sizes of less than 3 μm.